The utilization of suitable joining techniques is of decisive importance in the manufacture of radiation-emitting devices, particularly semiconductor devices in thin-film technology, and organic light-emitting diodes or so-called OLEDs.
The utilization of thin-film technology in radiation-emitting semiconductor devices is suitable, among other things, for the manufacture of light-emitting diodes with IR-, UV- or visible spectrum and of laser diodes (vertical cavity surface-emitting lasers or vertical external cavity surface-emitting lasers).
Thin-film light-emitting diode chips are described, for example, in U.S. Pat. No. 6,878,563 B2, WO 02/13281 A1 and EP 0905797 A2.
In the manufacture of radiation-emitting semiconductor devices in thin-film technology, a desired semiconductor structure is initially applied onto an epitaxial substrate. Subsequently, the epitaxial layer needs to be transferred to a carrier body (equivalent substrate). During this transfer, the epitaxial semiconductor heterostructure is bonded to the equivalent substrate with the aid of a joining technique. The growth substrate is then removed.
In addition to the mechanical stability of the joining technique, other parameters are also of decisive importance. The optoelectronic layer usually needs to be coupled to the equivalent substrate in an electrically or thermally conductive fashion. This is why metallic bonds are particularly suitable in this respect.
Until now, semiconductor heterostructures were usually bonded to the equivalent substrate by soldering (eutectic bonding) or adhesive bonding. A metallic bond produced by soldering is preferred because such a bond is more suitable due to its electrical and thermal conductivity. However, molten metals as they are produced, e.g., in soldering processes, can attack adjacent functional metal layers such as reflective layers or electrical contacts. Consequently, suitable blocking layers need to reliably separate the joining zone from functional layers or functional zones, respectively. However, the utilization of such blocking layers can create problems. Blocking layers can lead to dewetting of the solder and therefore reduce the adhesion. This is why the utilization of the soldering technique usually requires complex layer and material combinations.
The utilization of joining techniques in the manufacture of organic light-emitting diodes, in contrast, concerns the required encapsulation of these devices. Organic light-emitting diodes usually feature materials that need to be protected from environmental influences by means of an encapsulation. For this purpose, a layer is frequently bonded to another cover-like layer by means of a joining technique such that the actual organic light-emitting diode structure is hermetically encapsulated between the layers.
Adhesive bonding techniques as they are frequently utilized in the manufacture of organic light-emitting diodes are characterized by simple processing steps. However, they do not always provide the desired durability or impermeability, respectively.